The invention relates to a method of operating an externally ignited, piston-type internal-combustion engine having electromagnetic valve drives for operating the cylinder valves which are fully variably controllable by an electronic engine control for adapting their timing to varying operational conditions. The engine further has a fuel injection device for the individual cylinders.
In internal-combustion engines of the above-outlined type an ignition failure may cause damage to an exhaust gas catalyst of the engine, because an uncombusted charge is admitted to the exhaust gas system. In case of an injection failure, unintended air is admitted to the exhaust gas system, causing the catalyst control to enrich the fuel supplied to the other cylinders. Such an occurrence may have an adverse effect on the emission and also on the catalyst.